1. Field of the Invention
This invention relates to modified water soluble salt precoats for use in the cold drawing of steel wire.
2. Background of the Invention
Water soluble salt coatings are often applied to steel wire in the form of aqueous solutions prior to drawing. The solution-coated wire is dried and the resulting salt coated wire is then drawn through conventional reducing dies using dry soap lubricants--a process well-known to this art. The water soluble salt coating acts as a lubricant carrier, pulling the dry soap box lubricant into the dies, thus providing lubrication. These dried-in-place, water soluble salt coatings have proven to be superior to other conventional coatings such as lime or borax coatings because of their improved ability to carry lubricant into the dies. A typical soluble salt composition used for the coating of steel (usually stainless steel) wire contains both sodium sulfate and borax. Such soluble salt compositions provide coatings with excellent crystalline structure, resulting in good soap lubricant pick-up when the coated wire is passed through a soap box, and therefore good drawability. However, such salt coatings are prone to excessive moisture absorption upon exposure to ambient air, particularly when exposed to air having high humidity. Such moisture absorption seriously interferes with, or even prevents, the drawing of the coated wire. On the other hand, soluble salt coatings which provide low moisture absorption provide little or no crystalline structure (i.e. amorphous or glaze type coatings) and are significantly inferior in both lubricant pick-up and drawability. This Hobson's choice problem has not previously been solved.